1. Field of the Invention
The present invention relates to an electron generating apparatus constituted by arranging a plurality of surface-conduction emission devices on a substrate, a method of adjusting the characteristics of the electron generating apparatus, a method of manufacturing the electron generating apparatus, and an image forming apparatus using the electron generating apparatus.
2. Related Background Art
Conventionally, two types of devices, namely thermionic and cold cathode devices, are known as electron-emitting devices. Examples of cold cathode devices are surface-conduction emission devices, field emission type emission devices (to be referred to as FE type devices hereinafter), and metal/insulator/metal type emission devices (to be referred to as MIM type devices hereinafter).
Known examples of the FE type devices are described in W. P. Dyke and W. W. Dolan, xe2x80x9cField Emissionxe2x80x9d, Advance in Electron Physics, 8,89 (1956) and C. A. Spindt, xe2x80x9cPhysical properties of thin-film field emission cathodes with molybdenum conesxe2x80x9d, J. Appl. Phys., 47,5248 (1976).
A known example of the MIM type devices is described in C. A. Mead, xe2x80x9cOperation of Tunnel-emission Devicesxe2x80x9d, J. Appl. Phys., 32,646 (1961).
A known example of the surface-conduction emission devices is described in, e.g., M. I. Elinson, Radio. Eng. Electron Phys., 10 (1965) and other examples to be described later.
The surface-conduction emission device utilizes the phenomenon that electron emission is caused in a small-area thin film, formed on a substrate, by passing a current parallel to the film surface. The surface-conduction emission device includes devices using an Au thin film (G. Dittmer, xe2x80x9cThin Solid Filmsxe2x80x9d, 9,317 (1972)), an In2O3/SnO2 thin film (M. Hartwell and C. G. Fonstad, xe2x80x9cIEEE Trans. ED Conf.xe2x80x9d, 519 (1975)), and a carbon thin film (Hisashi Araki, et al., xe2x80x9cVacuumxe2x80x9d, Vol. 26, No. 1, p. 22 (1983)), and the like, in addition to an SnO2 thin film according to Elinson mentioned above.
FIG. 27 is a plan view of the surface-conduction emitting device according to M. Hartwell et al. as a typical example of the structures of these surface-conduction emission devices. Referring to FIG. 27, reference numeral 3001 denotes a substrate; and 3004, a conductive thin film made of a metal oxide formed by sputtering. This conductive thin film 3004 has an H-shaped pattern, as shown in FIG. 27. An electron-emitting portion 3005 is formed by performing an electrification process (referred to as an energization forming process to be described later) with respect to the conductive thin film 3004. Referring to FIG. 27, a spacing L is set to 0.5 to 1 [mm], and a width W is set to 0.1 [mm]. The electron-emitting portion 3005 is shown in a rectangular shape at the center of the conductive thin film 3004 for the sake of illustrative convenience, however, this does not exactly show the actual position and shape of the electron-emitting portion.
In the above surface-conduction emission device by M. Hartwell et al., typically the electron-emitting portion 3005 is formed by performing the electrification process called the energization forming process for the conductive thin film 3004 before electron emission. According to the energization forming process, electrification is performed by applying a constant DC voltage which increases at a very slow rate of, e.g., 1 V/min, to both ends of the conductive thin film 3004, so as to partially destroy or deform the conductive thin film 3004 or change the properties of the conductive thin film 3004, thereby forming the electron-emitting portion 3005 with an electrically high resistance. Note that the destroyed or deformed part of the conductive thin film 3004 or part where the properties are changed has a fissure. Upon application of an appropriate voltage to the conductive thin film 3004 after the energization forming process, electron emission is performed near the fissure.
The above surface-conduction emission devices are advantageous because, of cold cathode devices, they have a simple structure and can be easily manufactured. For this reason, many devices can be formed on a wide area. As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the present applicant, a method of arranging and driving a lot of devices has been studied.
Regarding applications of surface-conduction emission devices to, e.g., image forming apparatuses such as an image display apparatus and an image recording apparatus, charged beam sources and the like have been studied.
As an application to image display apparatuses, in particular, as disclosed in U.S. Pat. No. 5,066,883 and Japanese Patent Laid-Open Nos. 2-257551 and 4-28137 filed by the present applicant, an image display apparatus using the combination of a surface-conduction emission device and a phosphor which emits light upon irradiation of an electron beam has been studied. This type of image display apparatus is expected to have more excellent characteristics than other conventional image display apparatuses. For example, in comparison with recent popular liquid crystal display apparatuses, the above display apparatus is superior in that is does not require a backlight since it is of a light emissive type and that it has a wide view angle.
The present inventors have examined cold cathode devices according to various materials, manufacturing methods, and structures, in addition to the above conventional devices. The present inventors have also studied a multi-electron-beam source in which a lot of cold cathode devices are arranged, and an image display apparatus to which this multi-electron-beam source is applied.
The present inventors have also examined a multi-electron-beam source according to an electric wiring method shown in FIG. 28. More specifically, this multi-electron-beam source is constituted by two-dimensionally arranging a large number of cold cathode devices and wiring these devices in a matrix, as shown in FIG. 28.
Referring to FIG. 28, reference numeral 4001 denotes a cold cathode device; 4002, a row wiring layer; and 4003, a column wiring layer. The row wiring layers 4002 and the column wiring layers 4003 actually have limited electrical resistances which are represented as wiring resistances 4004 and 4005 in FIG. 28. The wiring shown in FIG. 28 is referred to as simple matrix wiring. For the illustrative convenience, the multi-electron-beam source constituted by a 6xc3x976 matrix is shown in FIG. 28. However, the scale of the matrix is not limited to this arrangement, as a matter of course. In a multi-electron-beam source for an image display apparatus, a number of devices sufficient to perform desired image display are arranged and wired.
In the multi-electron-beam source in which the surface-conduction emission devices are wired in a simple matrix, appropriate electrical signals are supplied to the row wiring layers 4002 and the column wiring layers 4003 to output desired electron beams. When the surface-conduction emission devices of an arbitrary row of the matrix are to be driven, a selection voltage Vs is applied to the row wiring layer 4002 of the selected row. Simultaneously, a non-selection voltage Vns is applied to the row wiring layers 4002 of unselected rows. In synchronism with this operation, a driving voltage Ve for outputting electron beams is applied to the column wiring layers 4003. According to this method, a voltage (Vexe2x88x92Vs) is applied to the surface-conduction emission devices of the selected row, and a voltage (Vexe2x88x92Vns) is applied to the surface-conduction emission devices of the unselected rows, assuming that a voltage drop caused by the wiring resistances 4004 and 4005 is negligible. When the voltages Ve, Vs, and Vns are set to appropriate levels, electron beams with a desired intensity are output from only the surface-conduction emission devices of the selected row. When different driving voltages Ve are applied to the respective column wiring layers 4003, electron beams with different intensities are output from the respective devices of the selected row. Since the response of the surface-conduction emission device is high, the period of time over which electron beams are output can also be changed in accordance with the period of time for applying the driving voltage Ve.
The multi-electron-beam source having surface-conduction emission devices arranged in a simple matrix can be used in a variety of applications. For example, the multi-electron-beam source can be suitably used as an electron source for an image display apparatus by appropriately supplying an electrical signal according to image information.
As a result of extensive studies for improving the characteristics of the surface-conduction emission device, the present inventors found that an activation process in the manufacturing process was effective.
As described above, when the electron-emitting portion of the surface-conduction emission device is to be formed, a process (energization forming process) of flowing a current to the conductive thin film to locally destroy, deform, or deteriorate the thin film and form a fissure is performed. Thereafter, when the activation process is performed, the electron-emitting characteristic can be largely improved.
More specifically, the activation process is a process of performing electrification of the electron-emitting portion formed by the energization forming process, under appropriate conditions, to deposit carbon or a carbon compound around the electron-emitting portion. For example, a voltage pulse is periodically applied in a vacuum atmosphere in which an organic substance at an appropriate partial pressure exists, and the total pressure is 10xe2x88x924 to 10xe2x88x925 [Torr]. With this process, any of monocrystalline graphite, polycrystalline graphite, amorphous carbon, and a mixture thereof is deposited near the electron-emitting portion to a thickness of 500 [xc3x85] or less. These conditions are only examples and must be appropriately changed in accordance with the material and shape of the surface-conduction emission device.
With this process, comparing the electron-emitting portion with that before the activation process, the emission current at the same applied voltage can be increased typically about 100 times or more. After the activation process is completed, the partial pressure of an organic substance in the vacuum atmosphere is preferably reduced.
Therefore, in manufacturing a multi-electron-beam source in which a lot of surface-conduction emission devices are wired in a simple matrix as well, the activation process is preferably performed for each device.
In the multi-electron-beam source manufactured in the above manner, the emission characteristics of the electron sources vary due to variations during the process. If such devices are used to form a display apparatus, the variation in characteristics appears as a luminance variation. There are various factors affecting the electron-emitting characteristics of the respective electron sources of the multi-electron-beam source: variations in components of a material used for the electron-emitting portion, dimensional errors of the members of devices, nonuniform electrification conditions in the energization forming process, and nonuniform electrification conditions or atmospheric gas in the activation process. However, to eliminate all these factors, the most advanced manufacturing equipment and strict process management are required, and this increases the manufacturing cost to an impractical level.
The present invention has been made in consideration of the above conventional problem, and has as its object to provide an electron generating apparatus which eliminates variations in electron-emitting characteristics of a multi-electron-beam source caused by the above-described various factors, a method of adjusting the characteristics of the electron generating apparatus, a method of manufacturing the electron generating apparatus, and an image forming apparatus using the electron generating apparatus.
It is another object of the present invention to provide an electron generating apparatus which substantially equalizes the characteristics of a multi-electron-beam source by using a property unique to a surface-conduction emission device, a method of adjusting the characteristics of the electron generating apparatus, a method of manufacturing the electron generating apparatus, and an image forming apparatus using the electron generating apparatus.
In order to achieve the above objects, the present invention provides a method of adjusting characteristics of an electron generating apparatus having a multi-electron-beam source in which a plurality of surface-conduction emission devices are arranged on a substrate, and driving means for outputting a driving voltage to the multi-electron-beam source, comprising the steps of applying a characteristic measuring voltage to measure the characteristics of the plurality of surface-conduction emission devices, obtaining a reference value of the characteristics of the plurality of surface-conduction emission devices on the basis of the measured electron-emitting characteristics, and applying a characteristic shift voltage to a corresponding one of the plurality of surface-conduction emission devices such that the electron-emitting characteristics of the plurality of surface-conduction emission devices become values according to the reference value, wherein the characteristic shift voltage is higher than characteristic measuring voltage, and the characteristic measuring voltage is higher than the driving voltage.
Preferably, the characteristic shift voltage is applied in an atmosphere in which a partial pressure of an organic gas is not more than 10xe2x88x928 Torr.
The method can further comprise the steps of measuring the characteristics of the plurality of surface-conduction emission devices again after application of the characteristic shift voltage, and applying the characteristic shift voltage to the corresponding surface-conduction emission device again on the basis of a remeasurement result.
In the measuring step, an emission current emitted from the surface-conduction emission device can be measured every time the surface-conduction emission device is driven.
In the measuring step, a device current flowing in the surface-conduction emission device can be measured every time the surface-conduction emission device is driven.
In the measuring step, a light emission luminance of electron emission from the surface-conduction emission device can be measured every time the surface-conduction emission device is driven, and the measured luminance can be converted into a value corresponding to the emission current or the device current.
The present invention also incorporates a method of manufacturing an electron generating apparatus. According to the present invention, there is provided a method of manufacturing an electron generating apparatus having a multi-electron-beam source in which a plurality of surface-conduction emission devices are arranged in a matrix on a substrate, and driving means for outputting a driving voltage to the multi-electron-beam source, comprising the steps of forming electrodes and conductive films for the plurality of surface-conduction emission devices on the substrate, forming electron-emitting portions for the plurality of surface-conduction emission devices by performing electrification to the conductive films through the electrodes, activating the electron-emitting portions, applying a characteristic measuring voltage to measure characteristics of the plurality of surface-conduction emission devices, obtaining a reference value of the characteristics of the plurality of surface-conduction emission devices on the basis of the measured electron-emitting characteristics, and applying a characteristic shift voltage to a corresponding one of the plurality of surface-conduction emission devices such that the electron-emitting characteristics of the plurality of surface-conduction emission devices become values according to the reference value, wherein the characteristic shift voltage is higher the characteristic measuring voltage, and the characteristic measuring voltage is higher than the driving voltage.
Preferably, the characteristic shift voltage is applied in an atmosphere in which a partial pressure of an organic gas is not more than 10xe2x88x928 Torr.
The method can further comprise the steps of measuring the characteristics of the plurality of surface-conduction emission devices again after application of the characteristic shift voltage, and applying the characteristic shift voltage to the corresponding surface-conduction emission device again on the basis of a remeasurement result.
In the measuring step, an emission current emitted from the surface-conduction emission device can be measured every time the surface-conduction emission device is driven.
In the measuring step, a device current flowing in the surface-conduction emission device can be measured every time the surface-conduction emission device is driven.
In the measuring step, a light emission luminance of the phosphor member can be measured every time the surface-conduction emission device is driven, and the measured luminance can be converted into a value corresponding to the emission current or the device current.
The present invention also incorporates an electron generating apparatus and an image display apparatus themselves. The present invention provides an electron generating apparatus comprising a multi-electron-beam source in which a plurality of surface-conduction emission devices are arranged on a substrate, and driving means for driving the multi-electron-beam source on the basis of an image signal, wherein the electron generating apparatus is manufactured by the above-described method.
The present invention provides an image forming apparatus comprising the above-described electron generating apparatus, and a phosphor which emits light upon irradiation of an electron beam from the multi-electron-beam source.
In the present invention, before or after the electron-emitting characteristics of each surface-conduction emission device are measured, and before the characteristic shift voltage for changing the characteristics of the device is applied, the organic gas must be removed from the atmosphere around the device.
To prevent the characteristics of the device from being changed by the display driving pulse, the values of voltages applied to each surface-conduction emission device preferably satisfy the relationship: (peak value of display driving pulse) less than (applied voltage value in measurement) less than (peak value of memory waveform signal). The display driving pulse can also be referred to as a driving voltage. The applied voltage value in measurement can also be referred to as a characteristic measuring voltage. The memory waveform signal can also be referred to as a characteristic shift voltage.
The electron generating apparatus of the present invention can be used for EB (Electron Beam) drawing in the semiconductor manufacturing process.
In addition, the method of adjusting the characteristic of the electron generating apparatus of the present invention can also be used when the electron-emitting characteristics of the surface-conduction emission device are changed with the elapse of time after completion of the electron generating apparatus.
According to the present invention, variations in electron-emitting characteristics of the electron-emitting devices caused by various factors can be eliminated with a simple process.
According to the present invention, the characteristics of the electron-emitting devices can be substantially equalized using a property unique to the surface-conduction emission device.